25/20: The 25 greatest discoveries in astronomy and astrophysics of the 20th century

I will present my personal list of the 25 most important and influential discoveries in astronomy of the 20th century. I will analyse the papers that reported these discoveries by the year they occurred, the age of the discoverers and the country where the people worked. The decades 1911-20 and 1960s were the most productive of the 20th century, in spite of the arrival of computers and observatories in space. I suggest reasons for the decline in the rate of really important papers in the final two decades of the century.